This invention relates to a membrane based filtration device. More particularly it relates to a porous membrane system which allows for the filtration of products while controlling the transmembrane pressure in the device.
The inability to control transmembrane pressure (TMP) causes increased rates of fouling especially in liquids having high particulate and/or colloidal concentrations such as biological broths. The high fouling results in an inconsistent filtration flow from the system.
Various solutions have been proposed to overcome this issue. One has been to run the device at lower flow rates in order to reduce the TMP differential from the feedstream inlet to the feedstream outlet. Alternatively, limiting the feed end TMP has been suggested as an option. Both are unacceptable as they reduce the performance of the system.
Another approach has been to use shorter module lengths which has not been acceptable as short modules are uneconomical to manufacture and use.
A third approach has been to increase the pressure on the filtrate side of the membrane device. While this works to reduce the average TMP over the length of the device, it fails to reduce the TMP differential from the feedstream inlet to the feedstream outlet, leading to fouling at the inlet.
A fourth approach has been to use baffles on the shell side of a hollow fiber device in order to assist in the control of TMP. Such a device is difficult to manufacture and use and provides only limited TMP control, especially in fluids which contain a high concentration of solids.
Lastly, the use of a separate pre-clarification step, such as one using coarse clarification pads to remove most of the large debris has been used. This is not acceptable as it adds an additional step and equipment cost.
None of the current approaches have effectively controlled the TMP and fouling of the system in a systematic and organised fashion while providing high throughput. What is desired is a system which allows for the optimum clarification, filtration and/or purification of products with high throughput volumes and TMP control. The present invention provides such a system.
The present invention comprises a porous hollow fiber membrane and the use of coflow on the filtrate side of the membranes so as to provide for TMP control of the system. Preferably, the addition of one or more beads on the filtrate side further improves the TMP control. The beads may be inert or they may be active, in that they may be size excluding glass or resin, an affinity resin, hydrophobic interactive chromatography resins, or an ion exchange resin which may be used to purify the filtrate stream by removing either a select desired specie in the filtrate or by removing a select contaminant from the filtrate stream.
One preferred embodiment of the present invention comprises a microporous hollow fiber bundle, said bundle being within a housing, said housing having a feedstream inlet on one end of the bundle and a feedstream outlet on another end of the bundle, said inlet and outlet being in communication with the inner cavity of the lumens of the bundle, said housing having a filtrate area between the outer surface of the bundle and the housing wall, said filtrate area having an outlet at one end of the housing, said filtrate outlet being connected to a downstream outlet and a recirculation loop, said loop being connected to a filtrate inlet adjacent the opposite of the housing from the filtrate outlet so as to allow the coflow of fluid on the filtrate side of the bundle in order to control the TMP differential.
A further embodiment of the present invention comprises a porous hollow fiber bundle, either microporous or ultraporous, said bundle being within a housing, said housing having a feedstream inlet on one end and a feedstream outlet on another end, said inlet and outlet being in communication with the inner cavity of the lumens of the bundle, said housing having a filtrate area between the outer surface of the bundle and the housing wall, said filtrate area having an outlet, said filtrate outlet being connected to a downstream outlet and a recirculation loop, said loop being connected to a filtrate inlet at an end of the housing opposite that of the filtrate outlet inlet so as to allow the coflow of fluid on the filtrate side of the bundle and said filtrate area containing a series of beads which in combination with the coflow of fluid controls the TMP differential.
Another preferred embodiment of the present invention comprises a porous hollow fiber, said bundle being within a housing, said housing having a feedstream inlet on one end and a feedstream outlet on another end, said inlet and outlet being in communication with the inner cavity of the lumens of the bundle, said housing having a filtrate area between the outer surface of the bundle and the housing wall, said filtrate area having an outlet, said filtrate area containing a series of capture beads capable of selectively retaining a desired specie of the filtrate stream and said filtrate outlet being connected to a downstream outlet and a recirculation loop, said loop being connected to a filtrate inlet at an end of the housing opposite the end containing the filtrate outlet such that the beads in combination with the coflow of filtrate controls the TMP of the system.
A further preferred embodiment of the present invention comprises a microporous hollow fiber bundle capable of forming vortices within its lumens so as to reduce fouling, said bundle being within a housing, said housing having a feedstream inlet on one end and a feedstream outlet on another end, said inlet and outlet being in communication with the inner cavity of the lumens of the bundle, said housing having a filtrate area between the outer surface of the bundle and the housing wall, said filtrate area having an outlet, said filtrate area containing a series of capture beads capabie of selectively retaining a desired specie of the filtrate stream, said filtrate outlet being connected to a downstream outlet and a recirculation loop, said loop being connected to a filtrate inlet located in the housing at an end opposite that which contains the filtrate outlet in order to create a coflow of filtrate on the filtrate side of the membranes and wherein said loop has a pump and said loop and downstream connector are controlled by a valve for selection between the recirculating and the downstream direction.
An even further embodiment of the present invention comprises a porous hollow fiber bundle capable of forming vortices within its lumens so as to reduce fouling, said bundle being within a housing, said housing having a feedstream inlet on one end and a feedstream outlet on another end, said inlet and outlet being in communication with the inner cavity of the lumens of the bundle, said housing having a filtrate area between the outer surface of the bundle and the housing wall, said filtrate area having an outlet and said filtrate outlet being connected to a downstream outlet and a recirculation loop, said loop being connected to a filtrate inlet adjacent the end of the housing adjacent the feedstream inlet and the filtrate area having one or more capture beads capable of selectively retaining a desired specie of the filtrate stream as well as for assisting in the control of the TMP of the system.
Also disclosed is a method of controlling the TMP of a filtration system comprising the steps of introducing a feedstock into one or more hollow fiber membranes, passing filtrate through the wall of the lumen into a filtrate channel, passing at least a portion of the filtrate through a recirculation loop back into the filtrate channel so as to create a suitable transmembrane pressure within the filtrate channel adjacent the outer wall of the membranes and removing the filtrate from the recirculation loop after a desired period of time.
Moreover, there is disclosed a method of backflushing a porous hollow fiber filtration system, wherein the system comprises a porous hollow fiber bundle, either microporous or ultraporous, said bundle being within a housing, said housing having a feedstream inlet on one end and a feedstream outlet on another end, said inlet and outlet being in communication with the inner cavity of the lumens of the bundle, said housing having a filtrate area between the outer surface of the bundle and the housing wall, said filtrate area having an outlet, said filtrate outlet being connected to a downstream outlet and a recirculation loop, said loop being connected to a filtrate inlet at an end of the housing opposite that of the filtrate outlet inlet so as to allow the coflow of fluid on the filtrate side of the bundle and said filtrate area containing a series of beads which in combination with the coflow of fluid controls the TMP differential by the process of shutting off the feedstream to the housing, reducing the pressure on the feedstream side of the membrane to a level below that of the filtrate side and circulating a fluid through the recirculation loop at a pressure higher than that of the feedstream side of the membrane so as to backflush the membrane and remove any trapped contaminants within the membrane from the system.
Lastly, there is disclosed a method of controlling the TMP of a filtration system comprising the steps of introducing a feedstock into one or more hollow fiber membranes, passing filtrate through the wall of the lumen into a filtrate channel, wherein the filtrate channel is filled with one or more types or sizes of beads so as to create a suitable transmembrane pressure within the filtrate channel adjacent the outer wall of the membranes and removing the filtrate from the filtrate channel.